This invention relates to Ziegler-Natta catalyst systems which use an amino substituted silane electron donor as a co-catalyst component. The olefin polymers produced with such catalyst systems exhibit a desirable combination of high isotacticity and high polydispersity index.
The isotacticity of a polymer is important in determining its suitability for a given application. Isotacticity is often measured by determining the weight percent of xylene-soluble polymer at room temperature (XSRT) and subtracting this from one hundred percent. A high isotacticity of greater than 90 is preferred and greater than 95 is most preferred.
Polydispersity index (P.I.) is a measurement of the molecular weight distribution of a polymer. A broad molecular weight range distribution (a high P.I.&gt;4.0) provides improved melt strength, which is advantageous in thermoforming, film, and fiber formation operations. A high P.I. of 4.0 is indicative of a broad molecular weight distribution. Preferably the P.I. is&gt;4.5, most preferably 5.0 or greater.
Organosilane compounds have been used in catalyst systems (1) as an electron donor in the solid catalyst component comprising a halogen-containing Ti compound supported on an anhydrous activated Mg-dihalide compound and (2) as an electron donor with the co-catalyst component comprising an organometallic compound. Typically they are organosilane compounds having Si--OR, Si--OCOR or Si--NR.sub.2 bonds, where R is alkyl, alkenyl, aryl, arylalkyl or cycloalkyl having 1 to 20 carbon atoms and Si as the central atom. Such compounds are described in U.S. Pat. Nos. 4,180,636; 4,242,479; 4,347,160; 4,382,019; 4,435,550; 4,442,276; 4,465,782, 4,473,660; 4,530,912 and 4,560,671, where they are used as electron donors in the solid catalyst component; and in U.S. Pat. Nos. 4,472,524, 4,522,930, 4,560,671, 4,581,342, 4,657,882 and European patent applications 45976 and 45977, where they are used as electron donors with the co-catalyst.
U.S. Pat. No. 5,102,842 discloses trifluoropropyl-substituted silanes which may also contain a piperidinyl or pyrrolidinyl ring, such as 3,3,3-trifluoropropyl (pyrrolidyl)-dimethoxysilane and 3,3,3-trifluoropropyl (4-methylpiperidyl)dimethoxysilane. Even more recently, European Patent Publication No. 658,577 teaches that fiber prepared from propylene homopolymers polymerized using trifluoropropyl(alkyl)dimethoxysilane has a lower bonding temperature and wider bonding temperature window than fibers of propylene homopolymer polymerized using catalysts having conventional electron donors such as phenyltriethoxysilane, dicyclopentyldimethoxysilane and diphenyldimethoxysilane.
An object of this invention is to provide novel aminosilanes useful as electron donors in olefin polymerization catalyst systems. Another object of the invention is to provide an improved catalyst system which produces olefin polymers having a desirable combination of high isotacticity and high polydispersity index.